1. Field of the Invention
This invention concerns a heat processing apparatus, for example, a gas-heated soldering or desoldering tool using a liquefied gas as a heat source for thermally processing various works made of metals, synthetic resins or like other materials.
2. Description of the Prior Art
As a typical example of heat processing apparatus, electrically-heated soldering irons for bonding metal parts or members through fusion of soldering flux, have generally been employed so far because of their simple structure, small size and light weight, as well as easy handlability.
Although gas-heated type soldering irons have also been employed depending on the case, for example, in field works where no electric source is available at hand, their use is not so popular since they are relatively large in the size and heavy in the weight requiring a large volume of gas combustion chamber for the sufficient supply of combustion air, as well as of complicated mechanism for the adjustment of gas concentration and gas feed rate.
However, with the recent development in the integrated circuit industry, disadvantages of using the electrically-heated irons in soldering electronic components or the likes of IC chips have been closed up. That is, if the electrical insulation between the power supply circuit (heater wire, etc.) and the copper tip of a soldering iron is insufficient or degraded during long use, a leak current will flow from the tip to an IC work which may possibly provide a fetal damage to the work even if the current is of a slight value. This trend has increased remarkably as the structure of IC chips has become more and more fine and accurate at present.
In view of the above, while various counter-measures have been taken for improving the electrically-heated soldering irons in order to avoid such undesired current leakage, it seems to be inevitable so long as the soldering irons are operated on the electric power supply.
In the foregoing situation, use of gas-heated soldering irons has now been re-estimated. However, there are many problems in the gas-heated soldering irons when they are actually used for fabricating IC chips or the likes.
At first, generation and exposure of gas flames out of a soldering iron has to be avoided by all means because it may cause danger of fire accidents and also provide damages to the IC chips. Next, the size and the weight of the soldering iron have to be reduced as much as possible, bacause fine and delicate handling is required to the iron upon fabricating IC chips at high accuracy.
In order to dissolve the foregoing problems, a compact and flameless gas heating apparatus has been proposed, for instance, by Fujihara in U.S. Pat. No. 4133301 (issued on Jan. 9, 1979 and now assigned to the assignee of the present application).
Referring briefly to the gas heating apparatus in the form of a gas-heated soldering iron disclosed in the U.S. Patent (for instance, FIG. 9 and relevant descriptions in the specification), liquefied gas from a gas tank 114 is introduced from a needle valve 153 by way of a gas inlet pipe 116 to a tubular connector 140 where it is mixed with airs from air holes 104, and then supplied to a combustion chamber 102. The gas mixture is burnt completely in contact with the catalyst filled in the combustion chamber 102 and then exhausted through apertures 102 formed in the wall of the combustion chamber. The heat produced by the catalytic combustion of the gas mixture is transmitted by way of a heat conductor rod 108 to a tip 109 for use in heating a work to be fabricated.
In the proposed apparatus, the liquefied gas can be burnt completely and efficiently by the aid of the catalyst, as well as generation of gas flame to the outside of the apparatus can remarkably be reduced since the combustible gas is burnt throughly within the combustion chamber in contact with the catalyst and only the exhaust gas (CO.sub.2, H.sub.2 O) is discharged externally.
However, in the apparatus cited above, the catalyst is filled at random in a fiberous or amorphous form within the combustion chamber at a considerably high density and the gas mixture passes through the complicated shape of gaps through the packed catalyst in the combustion chamber. Consequently, when the gas passes through the combustion chamber, there arises a considerable loss in the gas pressure. The gas mixture is generally formed by attracting the surrounding air into a gas stream as it is jetted out from a gas tank through a nozzle at a certain velocity due to the pressure created upon spontaneous evaporization of the liquefied gas (so-called ejector effect). Accordingly, if there is a large gas pressure loss in the combustion chamber, the gas evaporizing velocity at the tank exit is decreased making it difficult to provide a gas mixture of a sufficient air-to-gas ratio. This results in somewhat incomplete combustion in the combustion chamber, whereby an exhaust gas still containing combustible gas is discharged through the exhaustion port and it may flame-up to the outside of the chamber.
Further, the gas mixture is ignited at the inlet of the combustion chamber and an additional air is introduced through an ignition port provided near the upstream end (inlet) of the combustion chamber so that the gas mixture may be ignited effectively. However, since there is a large flow resistance in the combustion chamber as described above, a considerable portion of the ignition gas flame does not direct to the catalyst in the chamber but wastefully escapes through the ignition port externally. Thus, the ignition flame, particularly, the top end thereof at a relatively high temperature can not be effectively utilized for heating the combustion catalyst and it takes a much stand-by time to reach a desired combustion temperature.
In addition, the gas flame may continue to be discharged through the ignition port during soldering operation, which is very dangerous and remarkably reduces the gas utilizing efficiency as well.